Acid refining of heater oil



Sept. 13, 1955 J. H. KRAUsE ACID REFINING oF HEATER- oIL Filed July 26, 1952 mmhm mkm .m6 mhd /\b.. mmbm. G /mm mv Y /mv mv rllLfl A||||P| 4, mm (n mkmm A mkmm vv NM mlm 5.5. mv /mumu /bv 5R55 w m@ m www Nh. .G m um QSQ SY ATTORNEY United States Patent Ofiiee Z ,7 i 7,859 Patented Sept. 13, 1955 ACID REFINING F HEATER 0E Jack H. Krause, Hammond, Ind., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application July 26, 1952, Serial No. 301,033 1 Claim. (Cl. 19e-35) This invention relates to the refining of straight run petroleum distillates boiling in the heavier-than-gasoline range. More particularly it relates to the production of a sweet, color stable good burning quality heater oil by the acid treatment of a sour, high sulfur virgin petroleum distillate boiling between about 300 and 650 F.

A very large demand exists for petroleum distillates which boil in the heavier-than-gasoline range, i. e., within the range between about 300 and 650 F. These distillates are used for illumination purposes, diesel fuel, jet plane fuel, etc. A particularly important use for these distillates is in domestic heating installations; oils for this purpose are generally known as burning oils, furnace oils, or heater oils.

Consumer demand has been forcing the petroleum industry to produce better quality domestic heating oils. At this time specifications for domestic heating oils require that the oil be sweet, substantially mercaptan-free as determined by the doctor test, or 0.5 by the so-called mercaptan number; also, the oils are required to have good color stability in storage-an acceptable oil has a color of about Saybolt; also, the oils are required to have low deposit-forming tendencies, particularly in the sleevetype burner. The Jungers burner is generally known to require oils of particularly low deposit-forming tendencies.

Many processes are known for the production of good quality heater oils. The most generally used process is acid treatment. The acid treating process involves the contacting of the raw distillate with a given amount of sulfuric acid of a particular concentration; the acid sludge which consists of spent acid and acid-soluble materials is separated from the treated oil and the treated oil is further treated to remove occluded acid and oil-soluble reaction products-usually by water washing and contacting with aqueous caustic solution.

The better known method for acid treating involves a twoistep operation. In the first step the raw distillate is contacted at a temperature between about 100 and 125 F. with acid sludge derived from the second step. The treated oil is separated from the acid sludge and is then contacted with fresh sulfuric acid at a temperature between about 100 and 125 F. The oil is separated from the acid sludge formed in the second step and is neutralized and water washed to produce the product oil. However, it has been found that this method of treating cannot meet all three product requirements, i. e., a sweet oil, a color stable oil, and low burner deposit producing oil when the raw distillate is derived from a high sulfur crude such as West Texas crude.

It is an object of this invention to produce a sweet, color stable good burning quality oil from a sour, high sulfur straight run petroleum distillate which boils in the heavierthan-gasoline range. Another object is to produce a heater oil suitable for use in domestic heating installa-V tions. A particular object of the invention is to produce a domestic heating oil from a sour, high sulfur straight run petroleum distillate boiling in the range between about 300 and 650 F. by the sulfuric acid treatment thereof.

The above objects and other objects not set out are attained by treating a sour, high sulfur straight run petroleum distillate which boils in the heavier-than-gasoline range in a first step with an amount that is effective to substantially sweeten said distillate of about to fresh sulfuric acid at a temperature between about and 175 F.; separating treated oil from acid sludge; ,treating in a second step said treated oil with an amount suicient to remove oil-soluble acid reaction products of about 90 to 100% fresh sulfuric acid at a temperature between about 90 and 130 F.; separating acid sludge from said oil to obtain a substantially neutral product oil is utilized in said first treating step.

The process of this invention is particularly beneficial when applied to petroleum distillates which boil in the heavier-than-gasoline range and which are derived by distillation of crude oil. These distillates are commonly known as straight run or virgin distillates. in general the heavier-than-gasoline boiling range distillates boil within the range of about 300 to 650 F. Although the process tent, i. e., distillates which contain more than about 0.3 weight percent sulfur. A preferred feed stock to this process is a sour, high sulfur straight run petroleum distillate which boils within the range of about 325 to 550 F. High sulfur crudes most California crudes provide distillates which are particularly suitable for treatment by this process.

It has been discovered that a product oil of the desired quality is obtainable only by the use of fresh sulfuric acid in each of two treating steps or contacting steps. distillate is contacted with a desired amount of fresh sulfuric acid in a first contacting step; the treated oil latter sources produce the so-called black sulfuric acid.

It has been found that the fresh sulfuric acid used in this process must have an H2504 concentration of between about 96 and 99 weight percent. Acids of different concentrations may be used in each contacting step, but it is preferred to use acids of the same concentration in each step.

The amount of fresh sulfuric acid used in the first contacting step is dependent somewhat on the mercaptan content, the total sulfur content, and aromatic hydrocarbon content of the raw distillate. In general the higher the mercaptan content the more acid that must be used in the first contacting step. In general when using y step is very low in mercaptan content and Iusually is substantially sweet.

The acid usage in the second contacting step is dependent primarily upon the amount of oil-soluble acid reaction products contained in the treated oil from the first contacting step. Sufficient acid must be used in the second contacting step to remove substantially all of said oil-soluble materials. In general it has been found that when treating a sour, high sulfur content raw distillate that between about 2 and 5 lbs. of acid must be used in the second contacting step per barrel of raw distillate charged to the process.

It has been found that the temperature of contacting has an extremely important effect on the color stability and the deposit-forming tendencies of the product oil. ln order to achieve the objects of the invention it is necessary to carry out the treating at different temperatures in the two contacting steps; furthermore, the temperatures used in each contacting step are related to each other. The first contacting step in the process of this invention is carried out at a temperature between about 145 and 175 F., and preferably between about 155 and 165 F. The second contacting step is carried out at a temperature between about 90 and 130 F., and preferably between about 100 and 120 F. lt has been found that the higher the temperature of operation 1n the first step, the lower the temperature of operation must be in the second step. That is, the lower temperature range in the second contacting step corresponds to the upper temperature range in said rst contacting step. Thus when treating an oil in the first step at about 170 F., the second step must be carried out at about 90 F.

The contacting in the first step of this process must be for a time that is effective to substantially sweeten the raw distillate. In general the contacting time in the first step will be between about 2 and 30 minutes, and preferably between about 5 and 15 minutes. The tlme of contacting in the second step must be for a time that is effective for removing substantially all of the oil-soluble materials formed in the first step. Normally the contacting time in the second step will be between about 5 and minutes.

The term acid sludge as used herein is intended to include acid, acid-soluble reaction products, and acidsoluble materials derived from the raw distillate or the treated oil.

The annexed drawing which forms a part of this spec1- lisation shows in schematic form one illustrative embodiment of the process of this invention.

In the drawing the sour distillate feed from source 11 is passed through line 12, heat exchanger 13, and line 14 into line 16. In this illustrative embodiment the feed is a sour, high sulfur distillate boiling between about 330 and 620 F. and having a mercaptan number of about 100 along with a total sulfur content of about 0.9 weight percent.

Black sulfuric acid derived from the reconcentration of weak acid obtained from the hydrolysis of acid sludge is passed from source 17 by way of valved line 18, heat exchanger 19, and line 21 into line 16. The acid used herein has an H2804 content of 97 weight percent and 8 lbs. of said acid are used per barrel of feed.

The feed and acid are given some intermingling in line 16 before entering treater 22. Treater 22 is a cylindrical vessel that is provided with a motor-driven stirrer. Motor 23 drives paddle 24. A paddle agitator is used herein in order to obtain efficient contacting of the acid and the feed. Other mechanical stirrers could be used such as propellers or rotary turbines. Also, it is possible to use other types of mixers such as knothole mixers. The temperature in treater 22 is maintained at about 160 F. The feed is heated in heat exchanger 13 to a temperature on the order of 160'J F., and the acid is heated in heat exchanger 19 to an elevated temperature. The temperature of the feed and the acid was so adjusted that the heat of the reaction of the acid and the feed will not raise the contents of treater 22 to a temperature above about 160 F. The contacting time of the feed and the acid in treater 22 is about 10 minutes.

The thoroughly intermingled feed, acid and reaction products are withdrawn from treater 22 by way of valved l line 26 and are passed into settler 27. Settler 27 is an inclined cylindrical vessel provided with two compartments. Acid sludge is withdrawn from the lower part of settler 27 by way of valved line 2S and is sent to acid recovery facilities not shown. The treated oil is withdrawn. from settler 27 by Way of valved line 29 and is passed through heat exchanger 31 and line 32 into line 33.

Black sulfuric acid from source 17 is passed through valved line 36, heat exchanger 37 and line 38 into line 33. In this illustration 3 lbs. of acid are used per barrel of feed charged to the process. The acid and treated oil are passed by way of line 33 into treater 41. Treater 41 is provided with a motor 42 which drives paddle .stirrer 43. Treater 41 is similar in construction to treater 22. The temperature of the treated oil is suitably adjusted in heat exchanger 31 and the temperature of the acid is suitably adjusted in heat exchanger 37. The temperature in treater 41 is maintained at about 100 F. The contacting time in treater 41 in this illustration is l0 minutes.

The thoroughly intermingled oil and acid sludge from treater 41 are passed by way of valved line 44 into settler 46. A lower layer of sludge is withdrawn from settler 46 by way of valved line 47 and is sent to acid recovery facilities not shown. The upper layer of oil is withdrawn from settler 46 and is passed by way of line 43 into coalescer 49.

Coalescer 49 is an upright cylindrical vessel filled with a coalescing medium which is acid resistant. Suitable coalescing mediums are steel wool, metal chain, carbon Raschig rings, Berl saddles, etc. ln this instance coalescer 49 was packed with steel wool. In coalescer 49 the pepper sludge and other occluded material is agglomerated and passes to the bottom of the coalescer. The sludge is withdrawn from coalescer 49 by way of valved line 51 and is passed to acid recovery vessels. The pepper sludge-free oil is passed out of coalescer 49 by way of line 52.

A dilute aqueous caustic solution, 10% NaOH, from source 53 is passed by way of line 54 into line 52. The aqueous caustic and oil are thoroughly intermingled in mixer 56. The contacting in mixer S6 is continued until a substantially neutral oil is obtained. The aqueous caustic-oil mixture is passed from mixer 56 by way of valved line 57 into settler 58. A lower layer of waste caustic solution is withdrawn from settler 58 by Way of valved line 59 and sent to sewage disposal not shown.

The neutralized oil in settler 58 contains dissolved and suspended aqueous caustic solution. This oil is passed from settler 58 by way of valved line 61 into salt drum 62. Salt drum 62 is an upright cylindrical vessel which is filled with coarse rock salt. Instead of a salt drum an efficient coalescer provided with excelsior, fiber glass, steel wool, etc. may be used to remove the aqueous caustic from the oil. Brine is periodically removed from the bottom of the salt drum by way of valved line 63. A dehydrated product oil is withdrawn from salt drum 62 by way of line 64 and is sent to storage not shown.

Instead of the coalescer 49 which has been described above, the pepper sludge and associated oil-soluble materials may be removed from the oil in line 4S by other methods. For example, the pepper sludge containing oil may be water washed with between about 20 and 100 volume percent of water. The oil separated from the wash water may then be neutralized by contacting with aqueous caustic solution as described above. The caustic may be removed from the neutral oil by a water washing operation instead of using salt drum 62.

Another method of neutralizing the oil in line 48 is the contacting thereof with fullers earth fines such as Attapulgus clay or acid treated clay, or the oil may be passed through a bed of basic minerals such as magnesium carbonate or hydroxide. The illustration described above is necessarily generalized and many items of process equipment such as pumps have been omitted. The addition of these miscellaneous items of equipment is a matter of ordinary technical skill.

The results obtainable by the process of this invention are illustrated below. The feed to the illustrative tests was a virgin heater oil derived from West Texas crude. This heater oil is extremely ditcult to sweeten by any of the known processes and in general is of mediocre burning quality after conventional acid treatment. The physical characteristics of the feed heater oil are set out below:

The color stability lon storage of the product oil was determined by means of a laboratory test. The results of this laboratory test are known as aged color. In this test 100 ml. of the oil are maintained in an open beaker for 20 hours at 200 F. At the end of this time the Saybolt color of the oil is determined. It has been found that an aged color of +15 Saybolt or better indicates that the oil will have a satisfactory color stability in commercial storage.

It has been found that sleeve-type burners in domestic heating installations are most markedly afected by the u presence of deposits formed during the burning of the oil. The Jungers burner is an example of an extremely sensitive sleeve-type burner. Because of this sensitivity the Jungers burner has been adopted by many reners as a standard test burner for determining the burning quality of domestic heating oils. A full scale test using the Jungers burner involves the burning of many gallons of oil and many days of operation. A simple laboratory procedure has been developed which adequately predicts the t results obtainable in the full size Iungers burner test. This laboratory method is known as the steel dish deposit test.

The steel dish deposit test is carried out as follows: An lS-S stainless steel dish is of 500 F. By means of a hot plate. The dish is saucershaped and has the following dimensions: Outside diameter, 2 inches; thickness at the edge, 5/16 inch; thickness at the center of the dish, 3/16 inch. The depression in the dish corresponds to a section of a sphere. The dish is provided with a thermocouple which permits the temperature of the dish to be measured. The dish is placed on a hot plate, the temperature of which is adjusted to maintain the dish at about 500 F. The oil to be tested is dripped at a substantially constant rate onto the dish. The rate of evaporation of the oil from the dish should be substantially equal to the rate of addition of the oil to the dish, i. e., the dish always contains a iilm of liquid oil. A 400 ml. sample of oil is used in each test and the oil is added dropwise to the dish at a rate of about 1 rnl. per minute. At the completion of the test the dish is removed from the hot plate and allowed to cool. 'The diiference in the weight of the dish before and after the test is called the steel dish deposit.

A large number of tests on many diiferent oils have been made and it has been found that an oil which gives a steel dish deposit of mg. will operate satisfactorily in a Jungers burner.

Test 7 The treating steps in all tests were carried out in a three maintained at a temperature necked bathed ask driven paddle stirrer. of stirring in a balled obtained in a large size ing plant.

In this test a run was made for the purpose of comparison. In this run an amount of raw distillate was contacted at F. with 10 volume percent of acid sludge derived from the second treating step. The raw distillate and acid sludge were stirred for 10 minutes. The treated oil was decanted from the acid sludge. Using the same type of contacting flask the treated oil was contacted at 125 F. with 98% black sulfuric acid in an amount of 6 lbs. per barrel of raw distillate. After a 10-minute contacting time the oil was separated from the acid sludge; this acid sludge was then used to treat additional amounts of raw distillates in other tests.

The oil was passed through a steel wool coalescer to remove pepper sludge. The coalesced oil was then washed at ambient temperature successively with 10 volume percent of water, 20 volume percent of dilute aqueous caustic solution, and again with about l0 volume percent of water. The neutral washed oil was dehydrated by passage through a glass wool coalescer.

The pertinent characteristics of the product oil from this test were determined to be:

which was provided with a motor It has been found that this type llask approximates the contacting commercial continuous acid treat- The above oil closely corresponds to oil produced by this technique in a large scale continuous acid treating nuit. 'The oil from this method of operation does not meet the standards set for highest quality domestic heating oil.

TestZ This test was carried out to determine the effect of using fresh acid in both contacting steps. Using the equipment and the nishing techniques described in Test 1, a sample of raw distillate was treated as follows: In the first step the raw distillate was contacted with 6 lbs/bbl. of raw distillate of 98% black sulfuric acid at a temperature of 125 F. The treated oil in the second step was contacted with 2 lbs/bbl. of 98% black sulfuric acid at a temperature of 125 F. The product oil from this method of treating had the following characteristics Mercaptan number 7 Saybolt color, initial +21 Aged color +19 Steel dish deposits, mg 4 Thus the use of fresh acid in both treating steps markedly improved the aged color and the steel dish deposits of the product oil, but did not produce a sweet oil.

Test 3 All of these runs were made v ized as described in Test 1. The results of these runs are shown in tabular form below:

Temperature, F. Saybolt Color Steel Dish Mereatan Deposits 1st step 2nd step Initial Aged mg' These data show that on this particular raw distillate that when operating at a second step temperature of 90 F. it is necessary to operate the rst step at about F. in order to obtain a sweet product oil. However, increasing the iirst step temperature to F. resulted in a marked decrease in color stability and such a large increase in steel dish deposits that the product oil no longer meets the specification of 10 mg. of deposits. The data also show that when operating on this particular raw distillate a product oil of just barely acceptable quality is obtained when using a rst step temperature of 170 F. and a second step temperature of 130 F. Further, the data show that when operating on this raw distillate a satisfactory product oil cannot be produced when using a second step temperature of 140 F.

The data above indicate that for a sour, high sulfur virgin petroleum distillate derived from West Texas crude which boils between about 325 and 550 F. the rst step treating temperature must be between about 150 and 170 F., and the second step temperature must be between about 90 and 130 F., with a temperature relationship as shown above.

The above tests show that the process of this invention will produce a sweet, color stable good burning quality oil from a sour, high sulfur petroleum distillate which boils in the heavier-than-gasoline range. The prior art processes operating on the same distillate cannot produce an oil which meets all the requirements of a satisfactory domestic heating oil.

Thus having described the invention, what is claimed is:

A process which comprises (1) treating a sour high sulfur virgin petroleum distillate boiling between about 325 and about 550 F. with fresh sulfuric acid, having a concentration between about 96 and 99 weight percent in an amount between about 4 and 10 pounds per barrel of said distillate, said treating being carried out at a temperature between about 150 and 170 F. for a time between about 5 and 15 minutes; (2) separating acid sludge formed in said treating from treated oil; (3) treating said treated oil with fresh sulfuric acid having a concentration of between about 96 and 99 weight percent in an amount between about 2 and 5 pounds per barrel of distillate charged to step (l), said treating being carried out at a temperature between about 90 and 130 F. for a time between about 5 and 15 minutes, the higher the temperature of treating used in step (l) the lower the temperature of treating using in step (3); (4) separating acid sludge formed in step (3) from oil', and (5) treating said oil from step (4) to produce a substantially neutral refined oil which refined oil is substantially sweet, color stable and of good burning quality.

References Cited in the le of this patent UNITED STATES PATENTS 2,035,349 Smith Mar. 24, 1936 2,043,936 Story lune 9, 1936 2,155,367 Scott Apr. 18, 1939 2,264,904 Lemmon et al. Dec. 2, 1941 2,286,344 Chechot lune 16, 1942 

